The H-350 handset, NSN 5965-01-128-3944, was made for the Air Force. It is now the standard handset for tactical field telephone sets. It is equipped with a six-pin plug connector, either SI-329/U or AP-116. The H-350 has a wider microphone frequency response range than the H-250 handset.

H-250

The H-250, NSN 5935-00-043-3463, is used on many tactical radios, including SINCGARS. It has a five-pin metallic connector plug, U-229A/U, NSN 5935-00-992-2035. Other plugs are obsolete.

Compatibility

The fly-in-the-ointment for these two handsets is compatibility.

In tactical field telephones the sixth pin, pin F, is needed for full-duplex telephone operation. Therefore, the five-pin H-250 is incompatible and only the H-350 can be used.

Radios equipped with a five-pin audio connector can use either the H-250 or the H-350. The sixth pin on the H-350 will do nothing--no harm, no foul.

SINCGARS radios are equipped with six-pin connectors. In SINCGARS, the F-pin is not used for audio. If you try to use the H-350 you will hear static and feedback whenever you try to use push-to-talk (PTT). Therefore, the H-350 cannot be used on SINCGARS.